This application relates to the drilling of wells in the production of oil, gas and other fluids from underground formations, and particularly to the stabilization of boreholes drilled for the production of hydrocarbons. It includes the treatment of shale and clay in situ to prevent swelling caused by the absorption of water from drilling fluids.
A good description of the problem which this invention addresses in the context of formation drilling may be found in an article by Thomas W. Beihoffer et al in the May 16, 1992 Oil and Gas Journal, page 47 et seq., entitled xe2x80x9cCationic Polymer Drilling Fluid Can Sometimes Replace Oil-based Mud.xe2x80x9d As stated therein, xe2x80x9c(S)hales can become unstable when they react with water in the drilling fluid. These reactive shales contain clays that have been dehydrated over geologic time by overburden pressure. When the formation is exposed, the clays osmotically imbibe water from the drilling fluid. This leads to swelling of the shale, induced stresses, loss of mechanical strength, and shale failure.xe2x80x9d Shale crumbling into the borehole (xe2x80x9csloughingxe2x80x9d) can ultimately place a burden on the drill bit which makes it impossible to retrieve.
Salts such as potassium chloride have been widely used in drilling treatments to convert the formation material from the sodium form by ion exchange to, for example, the potassium form which is less vulnerable to swelling; also the use of high concentrations of potassium salts affects the osmotic balance and tends to inhibit the flow of water away from the high potassium salt concentrations into the shale. However, it is difficult to maintain the required high concentrations of potassium salts in the drilling fluids. In addition, the physical introduction of such salts causes difficulties with the preparation of the viscosifying materials typically used for drilling. Inorganic salts can also have a harmful effect on the environment if released.
As background for the present disclosure, I have assembled prior art references representative of three general types of amine and quaternary ammonium cation sources which have been suggested for clay treatment in hydrocarbon recovery. These are (a) single-site quaternaries and amines, (b) compounds having a few (two to about six) amine or quaternary ammonium cation sites, which I have called xe2x80x9coligocationicxe2x80x9d, and (c) quaternary ammonium or amine polymers, which may have from about six to thousands of cationic sites. The entire specifications of all of the patents set forth below are incorporated by reference, as the cationic materials described therein are useful in my invention.
A. Single-Site Quaternaries and Amines: Brown U.S. Pat. No. 2,761,835, Brown U.S. Pat. No. 2,761,840, Brown U.S. Pat. No. 2,761,836, Himes et al U.S. Pat. No. 4,842,073, Thomas and Smith U.S. Pat. No. 5,211,239.
B. Oligocationics: Brown U.S. Pat. No. 2,761,843; Krieg U.S. Pat. No. 3,349,032.
C. Polycationics: Borchardt et al U.S. Pat. No. 4,447,342, McLaughlin et al U.S. Pat. No. 4,374,739 McLaughlin et al U.S. Pat. No. 4,366,071.
My invention includes the use of combinations of potassium formate with various cationic materials, for the treatment of clay and shale in subterranean formations during drilling and otherwise for the stabilization of clay and clay-containing shale. For purposes of this patent application, it should be noted that all of the above identified patents incorporated by reference address problems similar to the problem I address. Each of the patents employs cationic formation control additives for drilling fluids to help control the swelling and sloughing of shale and clay contacted by aqueous drilling and other formation treating fluids. The contexts of use of such additives and the techniques for employing them as described in those patents are entirely consistent with and compatible with my invention. That is, I employ my own combination of additives in drilling fluids and otherwise to treat shale and clay to control swelling and sloughing.
Although the entire specifications of the above listed patents are incorporated by reference, to help in defining the materials useful in the present invention, I refer specifically to parts of the above identified patents, namely:
Brown U.S. Pat. No. 2,761,835 columns 3-10, Brown U.S. Pat. No. 2,761,840 columns 5-6, Brown U.S. Pat. No. 2,761,836 columns 5-6, Himes and Vinson U.S. Pat. No. 4,842,073 columns 1-10, Thomas and Smith U.S. Pat. No. 5,211,239 columns 1-2, Brown U.S. Pat. No. 2,761,843 columns 3-6, Krieg U.S. Pat. No. 3,349,032 columns 3-12, McLaughlin et al U.S. Pat. No. 4,366,071 columns 7-14, and Borchardt et al U.S. Pat. No. 4,447,342 columns 17-20.